Ain’t no upsides without downsides:

1. RICOH GR III image quality is still about 10x better than iPhone Pro. Also, the RICOH GR III is the superior “standalone camera” by far. Superior high ISO, far sharper, more detail, and quicker controls (you can change exposure compensation much easier).
2. iPhone Pro photos are stuck in Camera Roll/iCloud: Benefit of shooting with a standalone digital camera is you still have access to the JPEG (or RAW) files. Of course you can still export your iPhone photos to your hard drive, but practically speaking, you won’t.
3. Processing and selecting photos on the iPhone isn’t as quick or efficient as using a laptop. The iPhone Photos app is really really great but if your ultimate goal is to focus on maximizing your photographic output, it seems that the iPhone is a bit of a golden cage.
4. iPhone gets upgraded too quickly: In another year or so there will be a new and upgraded iPhone Pro, which of course will have better photo capabilities and image quality. Having to think about always upgrade is a distraction. Also, I’m a bit skeptical about the longevity of iPhone photos for the long-term. For example my smartphone photos from 5 years ago now look really bad (aesthetics and image quality wise), but my photos shot on film, “standalone digital cameras”, still look great.

iPhone Pro is still great

By no means do I desire to disparage the iPhone Pro or Apple’s photo team. In fact, I think Steve Jobs, Jony Ive, and the Apple photos and design/engineering team has done the most to advance photography to the masses. The iPhone is the ultimate open access, egalitarian, and democratic form of photography and I love it!

Practical suggestion

Use RICOH GR III as your primary shooter. Use it with ERIC KIM NECK STRAP MARK III, and just always have it around your neck. The iPhone Pro can be your supplementary backup camera (or just your “single device” for mobile computing).